Statistics HW Help

Please help me with this statistics question. Its a multi part question and I have to get all of them right to get credit, but i keep getting it wrong and don't know why. Please tell me what I'm doing wrong and tell me what the correct answer(s) are. Thank you

Is there an association between the use of computerized system and hospital mortality? In a large-scale hospital study, the study investigator randomly sampled 35 hospitals from all hospitals in Texas. Within each of the sampled hospitals, 500 patients who were hospitalized during the past year were randomly chosen. Their medical records were retrieved and whether they died while hospitalized was noted. It was found that on average, hospitals (26 of them) in which health care information is gathered and stored on computers had a lower patient death rate than hospitals (9 of them) that still rely on the "paper" system (using paper forms and handwritten notes).

Part I

What kind of study is this?

A. An observational study.

B. An experiment.

C. None of the above.

I CHOSE A

Part II

What sampling method was employed in selecting the 17500 patients?

A. Simple random sampling.

B. Stratified random sampling.

C. Multistage sampling.

D. Systematic sampling.

I CHOSE B

Part III

Which of the following is the population of interest to the study investigator? Choose the most appropriate answer.

A. All hospitals in Texas.

B. All patients who were admitted to the 35 selected hospitals in Texas.

C. The 35 Texas hospitals that were selected in the study.

D. The 17500 patients whose medical records were retrieved in the study.

I CHOSE D

Part IV

Which of the following statements is correct about the average patient death rate of all Texas hospitals in which health care information is gathered and stored on computers?

A. It is a variable of interest.

B. It is a statistic.

C. It is a parameter.

I CHOSE B

Part V

What graphical display is appropriate for comparing the distribution of patient death rates between hospitals that use computer systems and those that rely on the paper system?

A. A scatterplot.

B. A bar chart.

C. A stem-and-leaf display.

D. Side-by-side boxplots.

I CHOSE B

Part VI

Mr. Prudence read about the study results and concluded from there that hospitals should adopt computerized automation of notes and records because it increases patients chance of survival. Which of the following is a correct statement about Mr. Prudence's conclusion?

A. It is a valid conclusion because the study was based on a very large number of patients.

B. It is a valid conclusion because the study results showed that hospitals which use computerized systems have a lower patient death rate.

C. It is an invalid conclusion because this study does not necessarily prove a causal relationship between the use of computerized system and hospital mortality.

D. Both A) and B)

I CHOSE C.